Control of Charge Transport and Intermolecular Interaction in Organic Light-Emitting Diodes by Dendrimer Generation

Abstract

A novel family of conjugated dendrimers is used as model compounds to explore the effect of intermolecular interactions on photo‐physical and transport properties. The Figure shows the third generation of the dendrimers. The dendrimer generation controls the degree of chromophore interaction, which leads to a unique correlation between the chemical structure of the molecules and the macroscopic device properties (see also inside front cover).

Exciton confinement in organic dendrimer quantum wells for opto-electronic applications

“…[1][2][3][4][5][6][7][8][9][10][11] Rather than employing a linear geometry like in polymers, dendrimers are based on a self-similar fractal branching geometry, where the amount of branching increases with the size of the molecule. Through elegant synthetic routes it has been possible to create large, almost nanoscale molecules with a wide range of functional properties ranging from molecular recognition, such as in drug delivery systems 1 to artificial light-harvesting antennae.…”

“…Through elegant synthetic routes it has been possible to create large, almost nanoscale molecules with a wide range of functional properties ranging from molecular recognition, such as in drug delivery systems 1 to artificial light-harvesting antennae. 3,4,9 A particularly interesting area of applications is in optoelectronic devices such as light-emitting diodes ͑LEDs͒, where dendrimers have been used both as emitting layers 6,7,10 and as charge transport layers. 11,12 The well defined chemical structure of dendrimers allows a systematic correlation to be drawn between the device properties and the dendrimer structure.…”

“…10,11 We found that the level of interaction between core chromophores in the solid state is reduced with increasing generation, resulting in a narrowing of the emission spectrum. At high generations the film and solution luminescence spectra become similar.…”

“…Localisation of excitations on the core means that inter-chromophore interactions ͑which can lead to undesirable formation of aggregates or excimers͒ are reduced, explaining why higher generations have purer solid state emission closely resembling the solution luminescence spectra. 10 One further remarkable consequence of this energy gradient built into the dendrimer is that the charge transport through dendrimer films occurs through the core chromophore units rather than through the dendrons, which act as insulators in this case. Increasing generation hence results in a slowing of charge transport and the generation can be used as a microscopic control of the charge carrier mobility.…”

Synthesis and Characterization of Linear, Branched and Hyperbranched Triphenylamine-Based Polyazomethines

“…TPA-based oligomers with linear, dendrimer or star-shaped architecture have been synthesized and studied for various applications as organic light-emitting materials or field-effect transistors and two-photon related applications [14][15][16][17][18][19][20][21][22][23], while TPA-based polymers have been studied due to their excellent hole-transporting capacity, low ionization potential, high quantum yield of photoluminescence and thermal stability [22][23][24][25][26][27][28][29][30][31][32] and all these properties are associated with TPA groups. Until now there are only a few reports about TPA-based PAMs and most of them are not fully conjugated polymers.…”